How are your fans connected? Directly to motherboard? Fan controller? Daisy chained off one plug?
Buildapc
Directly to the motherboard
In that case, I'd be inclined to agree with Rimu about it being PSU related. I'd recommend carefully inspecting your 24 pin power cable and motherboard plug to see if any of the pins are damaged. Also, if you can, try and give each individual wire a little tug. Sometimes the pin isn't locked in properly and when you plug the cable in, the individual pin will get pushed out.
It could be your PSU - https://www.reddit.com/r/MSI_Gaming/comments/17cyaj7/msi_x670e_tomahawk_fans_not_spinning/. If you have a multimeter you could check if the voltages on the PSU outputs are Ok.
I really hope that this isn’t the root cause, as it is also a new PSU… But I could just send it back and get a different one. I don’t have a multimeter. Do you have a recommendation for one that isn’t too cheap but not break the bank expensive?
Is there any fan control in the BIOS? Tried resetting BIOS settings to default?
Tried resetting the BIOS settings to default and the problem is persisting. The BIOS is not able to detect that any fans are connected despite them all being plugged in via their 3 or 4 pin header connectors
I think the board might just be defective.